This invention relates to a hydraulic snubber for a grapple and, more particularly, to a snubber including internally provided piston to assist in the snubbing action between the snubber housing and the associated clevises.
In the skidding of logs, a vehicle is provided having a rearwardly extending boom from which is suspended a grapple. The grapple requires freedom of movement in two mutually perpendicular vertical planes and this is provided by a housing equipped with shafts connected to the boom clevis at the top and the grapple clevis at the bottom. However, when the grapple is free, it requires snubbing against free pivotal movement otherwise it could cause injury to logging personnel and damage to the grapple itself by crashing into the boom. Therefore art workers have provided various kinds of snubbers and hydraulic snubbers have been particularly popular. One form of hydraulic snubber is seen in co-owned U.S. Pat. No. 4,609,081.
Also well known for a long time are snubbers with hydraulic "assists", i.e., pistons operating against confined friction discs in brake or clutch fashion. Normally, these have utilized an internal piston. These have been unsatisfactory because of leakage of the hydraulic fluid which could foul the friction disc and destroy or at least seriously inhibit the snubbing action. This has resulted in the provision of hydraulic-assist snubbers with external pistons as seen in U.S. Pat. Nos. 4,573,728 and 4,679,839.
However, the external piston variety also has problems; not only are they more complicated and therefore more expensive but there is a projection that can be damaged resulting in expensive down time of the grapple.
The instant invention provides an internal ring piston type of hydraulic assist grapple. The invention addresses and solves the problem of fluid leakage and the aggravation thereof resulting from the fact that workers in the field pump up the snubbers to great pressure which increases the chance of fluid leakage and also prevents the desired easy but restrained action of the grapple. These twin problems have been solved by the instant invention.
According to the instant invention, a novel passage is provided for the pressure fluid to move the internal piston and which incorporates a novel seal to prevent the undesirable leakage. The grease inlet fitting to the passage also provides for protection against excessive external pressure so as to minimize the chance of undesired leakage and also to restrict the degree of snubbing. Still further, the invention provides an arrangement where easy replacement of the friction discs is achieved.
Other objects and advantages of the invention may be seen in the detail of the ensuing specification.